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Chapter 1. Overview
1-43
Performance Monitor
Instruction cache throttling provides control of the MPC7400s overall junction
temperature by determining the interval at which instructions are fetched. This feature is
accessed through the ICTC register.
Chapter 10, òPower and Thermal Management,ó provides information about power saving
and thermal management modes for the MPC7400.
1.12 Performance Monitor
The MPC7400 incorporates a performance monitor facility that system designers can use
to help bring up, debug, and optimize software performance. The performance monitor
counts events during execution of code, relating to dispatch, execution, completion, and
memory accesses.
The performance monitor incorporates several registers that can be read and written to by
supervisor-level software. User-level versions of these registers provide read-only access
for user-level applications. These registers are described in Section 1.4, òPowerPC
Registers and Programming Model.ó Performance monitor control registers, MMCR0 or
MMCR1, can be used to specify which events are to be counted and the conditions for
which a performance monitoring interrupt is taken. Additionally, the sampled instruction
address register, SIA (USIA), holds the address of the Trst instruction to complete after the
counter overowed.
Attempting to write to a user-read-only performance monitor register causes a program
exception, regardless of the MSR[PR] setting.
When a performance monitoring interrupt occurs, program execution continues from
vector offset 0x00F00.
Chapter 11, òPerformance Monitor,ó describes the operation of the performance monitor
diagnostic tool incorporated in the MPC7400.
1.13 Differences between the MPC7400 and the
MPC750
The design philosophy on the MPC7400 is to change from the MPC750 base only where
required to gain compelling multimedia and multiprocessor performance. The MPC7400s
core is essentially the same as the MPC750s, except that whereas the MPC750 has a
6-entry completion queue and has slower performance on some oating-point
double-precision operations, the MPC7400 has an 8-entry completion queue and a full
double-precision FPU. The MPC7400 also adds the AltiVec instruction set, has a new
memory subsystem (MSS), and can interface to an improved bus, the MPX bus. Differences
are summarized in Table 1-7.